1. Field of the Invention
This invention relates to one-part compositions that cure by a hydrosilation reaction. More particularly, this invention relates to compositions that cure by a platinum group metal-catalyzed hydrosilation reaction and contain a catalyst complex that is inactive only in the absence of oxygen, SiH-reactive hydroxylated compounds and/or heat. Curing of the compositions is achieved by activating the catalyst, thereby initiating curing of the composition.
2. Background Information
Curable compositions containing polyorganosiloxanes or organosiloxane-modified organic polymers yield crosslinked products ranging from flowable gels to elastomers to resins and find use in a wide variety of applications. These compositions can be classified based on the reaction used to cure the compositions. One such class of compositions cures by a hydrosilation reaction that is catalyzed by a metal from the platinum group of the periodic table or a compound of such a metal. These metals include platinum, rhodium and palladium.
The advantages of a hydrosilation cure include not requiring the presence of moisture or excessively high temperatures to initiate the curing reaction. The curing reaction occurs when all of the reactants, namely an organic polymer or polyorganosiloxane containing at least two alkenyl radicals per molecule and a compound containing at least two silicon bonded hydrogen atoms per molecule, are combined with the hydrosilation catalyst under ambient conditions. The obvious disadvantage of this type of curable composition is its poor storage stability. If it is not convenient to prepare the composition just prior to use, one method for overcoming this disadvantage is to prepare a two part composition by packaging the hydrosilation catalyst and the compound containing the silicon-bonded hydrogen atoms in separate containers.
One-part curable compositions with storage stabilities ranging from days to months depending upon the temperature can be prepared using known platinum catalyst inhibitors such as acetylenic compounds and amines or by encapsulating the hydrosilation catalyst in a material that is melted or fragmented to release the catalyst when it is desired to cure the composition. Both of these methods have disadvantages associated with them, including increased cost, relative high curing temperature and/or extended curing times.
The effect of anaerobic conditions, i.e. the absence of molecular oxygen, on the platinum-catalyzed reaction between organohydrogensilanes and alkenes or monomeric organosilicon compounds containing ethylenic unsaturation is reported in the patent and journal literature. U.S. Pat. No. 4,578,497, which issued to Onpochenko and Sabourin on Mar. 25, 1986 reports that oxygen enhanced the rate of the platinum catalyzed hydrosilation of 1-alkenes with mono-, di- and trialkylsilanes to yield the corresponding tetraalkylsilanes.
L. Lewis and N. Lewis in the journal Chemistry of Materials (1989, 1, 106-14) report that the reaction between platinic chloride and dimethylethoxysilane does not occur in the absence of molecular oxygen.
An article by L. Lewis [J. Am. Chem. Soc., 112, 16, 5998, (1990)] reports that formation of a catalytically active colloid by the reaction of a platinum compound with a stoichiometric excess of a silane or disiloxane containing silicon-bonded hydrogen atoms did not occur in the absence of molecular oxygen. The author considers the colloid to be the initiating species for hydrosilation reactions. Other hydrosilation reactions using the colloidal catalyst prepared using platinum or rhodium compounds are described by L. Lewis and R. Uriate in the journal "Organometallics" Vol. 9, pages 621-625, 1990.
Prior art studies on the effect of molecular oxygen on hydrosilation reactions catalyzed by platinum group metals and compounds of these metals did not utilize combinations of reactants capable of forming gels, elastomers, resins and similar high molecular weight crosslinked materials.
Organosiloxane compositions that cure upon heating by a platinum-catalyzed hydrosilation reaction and contain a "conventional" platinum catalyst and a phosphine or phosphite as the platinum catalyst inhibitor are claimed in U.S. Pat. No. 3,188,300 that issued to Chalk on Jun. 8, 1965. Organosiloxane compositions containing these compounds are alleged to be stable for periods up to 24 hours "or longer" at 25.degree. C. There is no teaching in this patent concerning the effect of or any advantage associated with preparing and storing the ingredients of the curable composition and the composition itself in the absence of oxygen or hydroxylated compounds that react with silicon-bonded hydrogen atoms.
Organosiloxane compositions that are stable in the absence of molecular oxygen but cure to yield elastomers or other useful materials in the presence of oxygen by a variety of reactions are known in the art. For example, U.S. Pat. No. 3,249,580, which issued to Beck on May 3, 1966 describes anaerobically stable compositions containing copolymers prepared by reacting a halogen-terminated polysilane containing at least two silicon-bonded hydrogen atoms per molecule with a member of a class of silanol-containing organosilicon compounds that includes polyorganosiloxanes.
U.S. Pat. No. 4,526,954, which issued to Williams on Jul. 2, 1988 describes linear and cyclic organosiloxane polymers that cure in the presence of oxygen but are stable under anaerobic conditions. The polymers are characterized by the presence of at least one 1,3-pentadienyl or 1,4-pentadienyl radical per molecule. The group containing this radical is bonded to silicon through a silicon-carbon bond. This patent also describes curable compositions containing the novel polymers in addition to fillers and curing catalysts.
Published European Patent Application No. 511,882-A1, published on Nov. 4, 1992, describes polyorganosiloxanes containing cyclopentadiene or cyclopentadienyl groups bonded to silicon directly or through a hydrocarbylene radical. The polyorganosiloxanes cure in the presence of moisture or oxygen.
One objective of this invention is to provide compositions that cure by a hydrosilation reaction and exhibit cure inhibition in the absence of molecular oxygen, SiH-reactive hydroxylated compounds and heat. A second objective is to provide a method for preparing these curable compositions using catalyst inhibitors that are active only under anaerobic conditions, in the absence of heat and hydroxylated compounds that react with the silicon-bonded hydrogen atoms present in the composition.